1. Field of the Invention
The present invention relates to a vehicle headlamp arranged to vary a luminous distribution pattern by movement of a movable shade.
2. Description of the Related Art
A typical vehicle headlamp is designed to emit a beam for use as a low or a high beam by causing a reflector to reflect light forward from a light source. As the required luminous distribution pattern of the low beam is different from that of the high beam, a light source bulb having two light sources or two light source bulbs are normally used for switching between low and high beams by switching the on and off conditions of the two light sources or the two light source bulbs.
Another known vehicle headlamp is arranged to switch beams with the use of a single light source. Particularly, this is often the case with a two-lamp type headlamp that inevitably employs a discharge bulb as a light source bulb.
A conventionally known method of switching beams in the case of such a single light source type is to move a shade as disclosed in Japanese Patent Laid-Open No. 2000-207918. According to this method, a movable shade having a cylindrical shade body and a shade leg portion extended downward from the shade body is arranged so that the movable shade is moved by a shade driving unit between two predetermined positions where a shading quantity of light incident on a reflector from a light source has two different values. The movement of the movable shade is made in longitudinal pivotal motion with a designated part of the shade leg portion as a pivotal center.
In such a vehicle headlamp having a movable shade of the sort mentioned above, direct light moving forward from the light source can be shaded by providing a fixed shade in front of the movable shade. Moreover, the appearance of a lighting device can be improved by making the movable shade and its peripheral structure difficult to see from the outside of the lighting device.
In this case, the fixed shade has to be provided in a position off its pivotal locus so that it does not interfer with the movable shade. However, as the maximum radius of the pivotal locus of the cylindrical shade body is considerably greater, the fixed shade inevitably becomes large-sized. The fixed shade also has to be positioned so as not to unnecessarily cover the light reflected from the reflector. Consequently, a space for use in disposing the fixed shade is greatly restricted and thus the freedom of design is considerably reduced.
The problem mentioned above generally develops not only when switching of low and high beams is carried out by moving the movable shade, but also when the luminous intensity distribution of the lighting device is varied by moving the movable shade.
The invention provides a vehicle headlamp so arranged as to vary the luminous intensity distribution of a lighting device by moving a movable shade, wherein the design freedom of a fixed shade provided in close vicinity to the front of the movable shade is improved.
A new configuration for the shade body of a movable shade is presented according to the invention.
According to the invention, a vehicle headlamp includes a light source, a reflector for reflecting light forward from the light source, a movable shade capable of shading part of light incident on the reflector from the light source, a shade driving unit for moving the movable shade between two predetermined positions where a shading quantity of light incident on the reflector has two different values, and a fixed shade provided in close vicinity to the front of the movable shade. The movable shade includes a shade body for surrounding the light source over a predetermined range and a shade leg portion extending from the shade body. The movable shade moves with a longitudinal pivotal motion with a predetermined region of the shade leg portion as a pivotal center. Lastly, the front end portion of the shade body is formed into a substantially semispherical shape, a slot extending along the pivotal face of the movable shade being formed in the front end portion thereof.
The xe2x80x98light sourcexe2x80x99 is not limited to any specific kind but may be, for example, the discharge light emitting portion of a discharge bulb or the filament of an incandescent bulb such as a halogen bulb.
The construction of the xe2x80x98movable shadexe2x80x99 is not limited to any specific embodiment as long as the movable shade is capable of shading part of light incident on the reflector from the light source bulb. The shade body and the shade leg portion may be formed integrally or separately.
The xe2x80x98two predetermined positions where a shading quantity of light incident on the reflector has two different values,xe2x80x99 may be the positions where a luminous distribution pattern for a low beam and a luminous distribution pattern for a high beam are formed by moving the movable shade to the respective predetermined positions, or a position where any other luminous distribution pattern is formed.
The xe2x80x98shade driving unitxe2x80x99 is not limited to any specific driving unit as long as it is so arranged to move the movable shade to one of two predetermined positions. This unit may employ a solenoid or a pulse motor.
The xe2x80x98longitudinal pivotal motionxe2x80x99 is such that the direction of its pivotal axis is not limited but may be any one of the lateral, vertical and oblique directions with the predetermined region of the shade leg portion as a pivotal center.
The phase xe2x80x98pivotal face of the movable shadexe2x80x99 means a plane crossing at right angles with the pivotal axis of the movable shade.
The phase xe2x80x98along the pivotal facexe2x80x99 means along a substantially arcuate curve formed as a line crossing the pivotal face of the movable shade and the front end portion of the shade body.
The vehicle headlamp according to the invention is arranged to vary the luminous intensity distribution of the lighting device by longitudinally pivoting the shade body that surrounds the discharge light emitting portion over a predetermined range. The movable shade has a shade leg portion extending from the shade body with the region near the lower end portion of the shade leg portion as the pivotal center. In addition, the front end portion of the shade body is formed into a substantially semispherical shape and a slot extending along the pivotal face of the movable shade is formed in the front end portion thereof, whereby the following operation/working-effect is achievable.
As the front end portion of the shade body is formed into the substantially semispherical shape, the maximum radius of the pivotal locus of the shade body can be made smaller in comparison with the conventional case where the front end portion thereof is formed into a cylindrical shape. Further, because as the slot is formed in the front end portion of the shade body, the shade body does not interface with the discharge bulb even though the diameter of the front end portion of the shade body is set at a considerably small value. The slot is formed so as to extend along the pivotal face of the movable shade, whereby the shade body is prevented from interfering with the discharge bulb even when the movable shade is caused to pivot. Therefore, the maximum radius of the pivotal locus of the shade body is considerably reducible as compared with the conventional shade body.
Consequently, the fixed shade provided in close vicinity to the front of the movable shade can be formed considerably smaller in size. Thus, a greater space for use in disposing the fixed shade can be secured within an allowable range of refraining from unnecessarily shading the light reflected from the reflector.
In the vehicle headlamp arranged to vary the luminous intensity distribution of the lighting device by moving the movable shade according to the invention, the design freedom of the fixed shade is enhanced.
In the vehicle headlamp according to the invention, the inertial load applied to the shade body when the movable shade is caused to pivot is decreased because the shade body is smaller in size than conventional shades, and thus, it is possible to reduce the load of the shade driving unit.
With the arrangement above, when the movable shade remains in the position where the shading quantity has a relatively large value, the diameter of the shade body is minimized by making the center position of the imaginary semispherical surface formed by the front end portion of the shade body conform to the position of the light source. Consequently, the design freedom of the fixed shade is enhanced further.
With the arrangement above, when the movable shade remains in the position where the shading quantity has a relatively large value, the diameter of the shade body is reduced further by passing the front end portion of the light source bulb through the slot formed in the front end portion of the shade body and extending the front end portion thereof ahead on the front end portion of the shade body. Consequently, the design freedom of the fixed shade is further enhanced.
With the arrangement above, the rigidity of the shade body is increased by forming a step portion in the front end portion of the shade body in such a way as to surround the slot. It is then possible to not only enlarge the opening area of the slot to that extent but also to decrease the thickness of the shade body.